1. Field of the Invention
The present invention relates to a supervisor handover on a Bluetooth high rate subnet, and in particular to a method capable of reducing supervisor handover time by using information on each member of a Bluetooth high rate subnet supervisor and selecting a candidate supervisor prior to a supervisor handover, and therefore effectively performing the supervisor handover.
2. Description of the Related Art
Bluetooth is a short-range wireless communication technology intended to replace a complicated cable connection among devices with a wireless connection among Bluetooth-enabled digital devices such as a printer, a personal digital assistant (PDA), a desktop, a facsimile, and a keyboard. A basic unit of the Bluetooth networking is a piconet comprising the Bluetooth enabled devices of a master to initiate data transaction and slaves to respond to the master in the Bluetooth network. Up to seven active slaves can be set to communicate with one master. Also, either the master or the slave of one piconet can be designated as a master for another piconet. Multiple piconets with overlapping coverage areas form a scatternet.
The Bluetooth technology provides a relatively fast transfer speed with low power consumption. In practice, for the devices within 10 m distances, 1 Mb/s transfer speed is enough to transfer and receive data. However, as the transfer of a large-capacity data such as a voice data or an image data is recently increasing, the transfer speed is required to be faster.
Accordingly, respective Bluetooth Special Interest Group (SIG) WGs (Working Groups) are working on a Bluetooth high data rate specification which is extended from the established Bluetooth specification. Hereinafter, the established Bluetooth version 1.1 is referred to as a “Low Rate (LR) mode” or a “Frequency Hopping (FH) mode”, and the high data rate specification is referred to as a “High Rate (HR) mode”. With the HR mode, the data transfer speed is estimated to be improved up to 12 Mb/s.
A HR channel for the HR mode may be formed with the conventional Bluetooth FH piconet channel. Accordingly, a HR subnet network is configured as a subnet of a FH piconet. At the same time, devices in the FH piconet can configure the HR subnet within the Bluetooth FH piconet by configuring the HR channel.
FIG. 1 is a diagram depicting an example of the FH piconet. Referring to FIG. 1, FH piconet is comprised of a master M and slaves S1˜S7. The master M and the slaves S1, S2 comprise one HR subnet, and the slaves S3, S4, S5 comprise another HR subnet. In the FH piconet, more than two HR subnets can be configured. The devices in the same HR subnet can directly communicate with each other on the HR channel.
The master of the FH piconet does not have to be included in the HR subnet, but is only concerned in configuration of the HR subnet. Instead, the HR subnet includes a HR supervisor. Referring to FIG. 1, on the HR subnet comprised of the master M and the slaves S1, S2, the master M is the supervisor. On the HR subnet comprised of the slaves S3, S4, S5, the slave S4 is the supervisor. When the HR subnet includes the master M, the master M usually functions as the HR supervisor.
Different from the master M, the HR supervisor does not regulate traffic in real time. The supervisor is responsible for link management. In detail, the supervisor enhances a transaction between the FH mode and the HR mode, reports a configuration change of the HR network such as a joining of a new device, and maintains a list of active devices in the HR subnet.
The devices in the HR subnet (hereinafter, called “HR members”) still hold their function in the FH piconet. The piconet master recognizes the slaves in the HR subnet as having a power-saving mode such as a Park mode, Hold mode, and Sniff mode. The devices in the HR subnet communicate on the HR channel while not communicating on the FH channel, and periodically scan the FH piconet channel in order to synchronize with the FH channel. Accordingly, the piconet master continuously controls all of the devices in the FH piconet.
In the communication on the HR channel, Medium Access Control (MAC) is performed via a token mechanism. The token mechanism is a priority scheme which provides the right to transmit on the HR channel by allowing a priority slot, or a token, to one of the members of the HR subnet; the token mechanism is introduced to guarantee a Quality of Service (QoS), and to provide transmission services such as synchronous, asynchronous and isochronous transmission service.
The HR devices use the token mechanism and communicate in a peer-to-peer basis without any intervention of the HR supervisor. However, the HR supervisor has to hold addresses of active members constantly, and when the supervisor is changed, the previous supervisor returns to the original state as a member of the FH piconet.
Even if there is no HR supervisor, the communication on the HR network is possible in this case, but the priority slot cannot be allocated to any device. As a result, in any slot regardless of the priority, the traffic can be initiated. It is not possible to add a new device or a new logic link to the network, because the slot structure of the network is lost. Accordingly, the FH master periodically broadcasts information about the current HR supervisor to every member of the HR subnet and transmits a poll message to the HR supervisor. If the supervisor does not respond within a timeout period, the FH master detects an absence of the supervisor.
Any device in the HR network can be the HR supervisor, and the HR supervisor is selected by the FH master. If the absence of the HR supervisor is detected, the FH master selects a device having a smallest Device Control Point (DCP) address as a new HR supervisor among the members which are capable of communicating with the other entire members. The DCP address is allocated by the FH master in an ascending order from “1”, when each device is connected to the HR network. A procedure of selecting the new supervisor due to the absence of the current supervisor is referred to as a HR supervisor handover and can be caused by several reasons such as the HR network disconnection of the current supervisor (HR synchronization timeout) or a request for Link Message Protocol (LMP) HR handover due to the joining of a new device having a better capability for the supervisor. Since every member in the HR network holds information on the configuration of the HR network, any member can be the supervisor.
According to the conventional method as aforementioned, upon the absence of the current HR supervisor, the master M retrieves the members of the HR subnet capable of communicating with the other members and selects the new supervisor among them. At this time, the master notifies the member having the smallest DCP address of the supervisor handover, and the notified member broadcasts an inquiry message to the other members. Based on responses from the members, it is determined whether the notified member is capable of communicating with the other members. If there is no response from any member, the notified member is not qualified for the supervisor. Then, the master notifies the member having the second smallest DCP address of the supervisor handover, and the notified member repeats the above procedure. This procedure is repeated over again until all of the members respond to the inquiry message or the inquiry message is broadcasted by all of the members. Accordingly, if there is no member capable of communicating with all of the members, the supervisor handover is finished and all of the HR members return to the FH piconet.
The DCP address indicates only the order of connection to the FH network of the devices, not the device capability or the location on the HR network. That is, the device having the smallest DCP address does not always have to be the best candidate for the supervisor. Therefore, in the supervisor handover, generally, the above procedure is repeated several times until the master selects the new supervisor. After the new supervisor is selected, a synchronization is newly performed by the new supervisor and the HR network is stabilized. Consequently, a long absent period of the supervisor raises problems such as service interruption.